This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the maximum load is 5 A at 40 V.
This dimmer with a unijunction transistor and SCR appeared in Radio Electronics magazine in March...
This sophisticated model railway controller was found in the November 1969 issue of Radio...
In the MEMs line of the ST available on Mouser Electronics we highlight the MP23AB01DH audio...